1. Technical Field
The present invention generally relates to emission control systems and, more particularly, to oxygen sensor-based emission control systems for automotive vehicles.
2. Discussion
Operation of an internal combustion engine causes certain exhaust elements to be generated. For instance, hydrocarbons (HC) and nitrous oxide (NOx) emissions are produced. Certain air quality management plans dictate that such emissions be controlled to within pre-selected limits.
To reduce the amount of undesirable emissions passing through an engine exhaust system to the atmosphere, modern motor vehicles employ a catalytic converter. The catalytic converter fosters a reaction wherein undesirable emission elements are converted to different elements prior to their passage to the atmosphere. To monitor the efficiency of the catalytic converter, sensors are sometimes employed.
For example, an oxygen sensor may be disposed upstream of a catalyst in the catalytic converter so that the nature of the exhaust gasses entering the catalyst may be determined. If the constituents of the exhaust gas are not within a desirable range, the output of the oxygen sensor is used to modify the fuel-to-air ratio within the engine. Often, this entails increasing or decreasing the amount of fuel injected by the fuel injectors in the engine. As a result, the constituents within the exhaust gas are modified.
Similarly, by disposing an oxygen sensor downstream of the catalyst, the constituents of the exhaust gas exiting the catalyst can be learned. If the constituents are not within the desired range, the fuel-to-air ratio within the engine can be modified. Further, by placing a first oxygen sensor upstream of the catalyst and a second oxygen sensor downstream of the catalyst, the nature of the exhaust gas through the catalyst can be learned. As such, greater control of the fuel-to-air ratio within the engine may be exercised to modify the exhaust constituents.
In some automotive vehicles, a second catalyst brick is employed in the catalytic converter can downstream of the first catalyst brick. In combination with such an arrangement, a first oxygen sensor has been placed upstream of the first catalyst and a second oxygen sensor has been disposed downstream of the first catalyst and upstream of the second catalyst. This is the so-called "mid-brick" position. While this configuration has provided beneficial results for learning the constituents through the first catalyst and entering the second catalyst, there is room for improvement in the art.
For example, it would be desirable to provide a configuration that enables learning of the constituents through the second catalyst thereby enhancing control of the level of nitrous oxide passing through the system.